121–130 of 183 posts
I find it very interesting that every time Dark Matter, a theory that actual physicists largely find very convincing, comes up a bunch of non-physicist HNers come out to explain why it doesn't make sense.
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Why isn’t it good for physics? It has found DM and can observe it via gravitational discrepancies, gets finally “solved” in this part. Does physics really need infinite modifications?
It’s not good because it means there is something in nature that we cannot understand and study, because we cannot in fact observe it directly. The gravitational discrepancies we have already, but without an explanation or observation, they’re not very satisfactory.
We can't observe anything "directly", other than the contents of our own minds. The "gravitational discrepancies" are an observation.
It seems to me (non-physicist, non-cosmologist) that DM proponents can't tell us what DM is, despite being able to observe it. The article's "nightmare" is that it might turn out to be impossible to do that in principle. To my mind, that would indeed be a nightmare; we would have to accept that there are limits to what we can learn about the Universe. I don't believe we have encountered any such limits before.
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> You don't seem to quite understand the current cosmological models. You don't need special cases for every galaxy. No, he's correct that each galaxy does need tuning. Specifically, the amount of DM and it's specific distribution is tuned to match each observation, which is what the OP said. > but it is also true that anything that has to do with galaxy/star formation is immensely complicated as it involves a lot of…
> the amount of DM and it's specific distribution is tuned to match each observation This is simply not true. No cosmological theory tries to explain why each star is in its exact observed location. They try to predict the statistics of galaxies, star formation, etc. If you run a simulation of the universe, beginning with very simple, random initial conditions, and then run physics forward for 13 billion years, you g…
This is actually exactly wrong. If you run LCDM for 13 billion years you don't get galaxies till much later than what we observe via say JWST. However, with MOND you predict early galaxies due to the higher force of gravity at distances causing earlier collapse.
Has anyone considered modeling the effect currently explained via dark matter as a new kind of force or field? Like a distinct force generated by mass and its relationship to space time?
This wouldn’t be modified gravity but a proposal for an entirely new force whose effect is what we currently explain with the “fudge factor” of dark matter.
From the rough picture I do have of dark matter this force would be one whose relationship to distance is different from the usual inverse square law that governs forces. That would be weird but maybe no weirder than particles that can never be detected or MOND.
I find it very interesting that every time Dark Matter, a theory that actual physicists largely find very convincing, comes up a bunch of non-physicist HNers come out to explain why it doesn't make sense.
It feels like this is implying that questioning is unscientific? I mean, I get being annoyed with laypeople but if you didn’t question the scientific consensus the historic record and the philosophy of science are against you.
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Probably because it's the only piece of evidence you can understand with just high school physics. Most laypeople have trouble understanding that the universe is not expanding from a single point, so how would they be able to understand what the cosmic background radiation is, much less why its angular power spectrum has peaks at particular positions? It's a common pattern with crackpots as well, that they focus on "…
Crackpots emerge when a conceptual model is weak. They don't care how strong a mathematical model is, which is why they ignore SM and other areas where "theory" literally means a mathematical model, and nothing else. Having a lot of crackpots proposing bad theories is a sign that your conceptual model is garbage, just a bad attempt to hand wave a bunch of math that happens to predict reality, and you should stop pret…
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> Specifically, the amount of DM and it's specific distribution is tuned to match each observation ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science?
Well, yes. That's because we have a pretty strong prior about the existence of planets orbiting stars. It was there before we started adding planets to explain the stars wobbles. With DM the rationale goes the other way around. What means it's not a solid explanation. That is perfectly fine, as long as proponents don't go saying it's settled knowledge and start fighting the people looking for alternatives. When they…
No it doesn't. We have strong priors that the movement of bodies is affected by gravity, and gravity comes from matter. When we see movement we cant' explain given the matter we can see, the most obvious explanation is matter we cannot see for some reason.
I find it very interesting that every time Dark Matter, a theory that actual physicists largely find very convincing, comes up a bunch of non-physicist HNers come out to explain why it doesn't make sense.
Earlier quoted context omitted.
> Specifically, the amount of DM and it's specific distribution is tuned to match each observation ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science?
> ...and? If we look at the way a star wobbles, then tune the amount and distribution of planets around it to fit, isn't that just science? That is science because gravity has been extensively tested and confirmed in that regime. Gravity on the scales where dark matter is relevant has not been tested to this extent, so we're just assuming our theory is correct in this new regime and thus inferring the DM distribution…
Couldn't we just as easily say the same about EM or any of the other forces?
The reason we think it is some kind of matter is because we know that matter interacts with gravity in ways that would explain our observations, as long as we assume that matter isn't visible for some reason. And it isn't like there aren't candidates even within the current standard model that might have the right properties.
> By contrast, modified gravity theories can match many of the predictions of DM theories using only direct observations of visible matter.
...and curve fitting. They keep having to add parameters to MOND to make it fit what we see and currently attribute to dark matter, like the bullet cluster. That's the physics equivalent of code-smell.
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You could read through the relevant Wikipedia pages for an overview: https://en.wikipedia.org/wiki/Dark_matter#Observational_evid...
Wikipedia is rarely a good introduction for laymen. It tends to be a great reference for people already in the field.
(One might remark that I'm just not intelligent enough to understand advanced mathematics, and they might be right...)